During the last three years, a laser scanning confocal microscopy facility has been established in the Laboratory of Cellular Hematology. Confocal microscopy is a state-of-the art technology that enhances the contrast and resolution of microscopic images by rejecting out-of-focus information. Thin optical sections of specimen are obtained, each image is stored on a computer, and the image series is reconstructed as a stereo or 3-dimension image. The facility has been used for the studies outlined below. 1. Cytoskeletal changes in chemoattractant-stimulated neutrophils. Specific fluorescent probes for filamentous actin are used to map the location of actin filaments during the activation of neutrophils with chemoattractants. Time course studies of the actin filament location and quantitative image analysis of the fluorescence signals are performed to determine the pattern of actin filament assembly and morphologic change during neutrophil stimulation. 2. Membrane antigen location during leukocyte migration. Fluorescent monoclonal antibodies to neutrophil plasma membrane antigens are used to detect the location of the antigens on neutrophils that have migrated in vitro through polycarbonate membranes to chemoattractants. Results using this technique were published this year (J. Immunol. 146: 949-957, 1991).